1. Background
The ability to manipulate characteristics of fiber quality in cotton through genetic engineering techniques would permit the rapid introduction of improved cotton varietes. Cotton fiber quality is conventionally measured in terms of characteristics of strength, length and micronaire (a measurement of fiber fineness).
In general, genetic engineering techniques have been directed to modifying the phenotype of individual prokaryotic and eukaryotic cells, especially in culture. Plant cells have proven more intransigent than other eukaryotic cells, due not only to a lack of suitable vector systems but also as a result of the different goals involved. For many applications, it is desirable to be able to control gene expression at a particular stage in the growth of a plant or in a particular plant part. For this purpose, regulatory sequences are required which afford the desired initiation of transcription in the appropriate cell types and/or at the appropriate time in the plant's development without having serious detrimental effects on plant development and productivity. It is therefore of interest to be able to isolate sequences which can be used to provide the desired regulation of transcription in a plant cell during the growing cycle of the host plant.
One aspect of this interest is the ability to change the phenotype of particular cell types, such as differentiated epidermal cells that originated in ovary tissue, so as to provide for altered or improved aspects of the mature cell type. In order to effect the desired phenotypic changes, transcription initiation regions capable of initiating transcription in early ovary development are used. These transcription initiation regions are active prior to the onset of pollination and are less active or inactive, before fruit enlargement, tissue maturation, or the like occur.
2. Relevant Literature
Methods and compositions for modulating cytokinin expression in tomato fruit are described in U.S. Pat. No. 5,177,307. U.S. Pat. No. 5,175,095 describes ovary tissue transcriptional promoters, including a pZ7 promoter active in ovule integument cells. The disclosure of both patents is hereby incorporated by reference. Neither patent describes a method for modifying a characteristic of cotton fiber quality.
A class of fruit-specific promoters expressed at or during anthesis through fruit development, at least until the beginning of ripening, is discussed in European Application 88.906296.4, the disclosure of which is hereby incorporated by reference. cDNA clones that are preferentially expressed in cotton fiber have been isolated. One of the clones isolated corresponds to mRNA and protein that are highest during the late primary cell wall and early secondary cell wall synthesis stages. John Crow Pro. Natl. Acad. Sci. (1992) 89:5769-5773. cDNA clones from tomato displaying differential expression during fruit development have been isolated and characterized (Mansson et al., Mol. Gen. Genet. (1985) 200:356-361: Slater et al., Plant Mol. Biol. (1985) 5: 137-147). These studies have focused primarily on mRNAs which accumulate during fruit ripening. One of the proteins encoded by the ripening-specific cDNAs has been identified as polygalacturonase (Slater et al., Plant Mol. Biol. (1985) 5:137-147). A cDNA clone which encodes tomato polygalacturonase has been sequenced (Grierson et al., Nucleic Acids Research (1986) 14:8395-8603). Improvements in aspects of tomato fruit storage and handling through transcriptional manipulation of expression of the polygalacturonase gene have been reported (Sheehy et al., Proc. Natl. Acad. Sci. (1988) 85:8805-8809; Smith et al., Nature (1988) 334: 724-726).
Mature plastid mRNA for psbA (one of the components of photosystem II) reaches its highest level late in fruit development, whereas after the onset of ripening, plastid mRNAs for other components of photosystem I and II decline to nondetectable levels in chromoplasts (Piechulla et al., Plant Mol. Biol. (1986) 7:367-376). Recently, cDNA clones representing genes apparently involved in tomato pollen (McCormick et al., Tomato Biotechnology (1987) Alan R. Liss, Inc., NY) and pistil (Gasser et al., Plant Cell (1989), 1:15-24) interactions have also been isolated and characterized.
Other studies have focused on genes inducibly regulated, e.g. genes encoding serine proteinase inhibitors, which are expressed in response to wounding in tomato (Graham et al., J. Biol. Chem. (1985) 260:6555-6560: Graham et al., J. Biol. Chem. (1985) 260:6561-6554) and on mRNAs correlated with ethylene synthesis in ripening fruit and leaves after wounding (Smith et al., Planta (1986) 168: 94-100). Accumulation of a metallocarboxypeptidase inhibitor protein has been reported in leaves of wounded potato plants (Graham et al., Biochem & Biophys. Res. Comm. (1981) 101: 1164-1170; Martineau et al., Mol. Gen. Genet. (1991) 228:281-286).
Genes which are expressed preferentially in plant seed tissues, such as in embryos or seed coats, have also been reported. (See, for example, European Patent Application 87306739.1 (published as 0 255 378 on Feb. 3, 1988) and Kridl et al., Seed Science Research (1991) 1:209-219).
Agrobacterium-mediated cotton transformation is described in Umbeck, U.S. Pat. Nos. 5,004,863 and 5,159,135 and cotton transformation by particle bombardment is reported in WO 92/15675, published Sep. 17, 1992. Transformation of Brassica has been described by Radke et al., (Theor. Appl. Genet. (1988) 75:685-694; Plant Cell Reports (1992) 11:499-505).
Transformation of cultivated tomato is described by McCormick et al., Plant Cell Reports (1986) 5:81-89 and Fillatti et al., Bio/Technology (1987) 5:726-730.